1. Field of the Invention
The present invention relates to a synchronous machine simulator and a synchronous machine simulation method for simulating a synchronous machine in an electrical power system.
2. Description of the Prior Art
FIG. 18 is a block diagram showing a conventional synchronous machine simulator. In FIG. 18, the reference number 1 designates an analogue to digital (A/D) conversion section for converting real instantaneous values of both a three phase analogue voltage and three phase analogue current into digital values thereof, and the reference number 2 denotes a d-q axis conversion section for converting the three phase voltage and the three phase current in digital form, that are converted in the A/D conversion operation executed by the A/D conversion section 1, into a direct voltage and a direct current and for outputting the direct voltage and the direct current. The reference number 3 indicates an exciting system calculation section for calculating an exciting voltage and an exciting current of the synchronous machine based on the three phase voltage and the three phase current that have been converted by the A/D conversion section 1. The reference number 4 designates a magnetic flux calculating section for calculating a variation part of the magnetic flux of the synchronous machine based on the direct voltage and the direct current outputted from the d-q axis conversion section 2 and the exciting voltage and the exciting current outputted from the exciting system calculation section 3. The reference number 5 denotes a shaft system calculation section for calculating a variation part of a shaft torque of the synchronous machine by using the variation part of the magnetic flux outputted from the magnetic flux calculation section 4 and the variation part of the shaft torque of a speed governor. The reference number 6 denotes a speed governor calculation section for calculating a variation part of the speed governor based on the variation part of the shaft torque. The reference number 7 designates an instruction value calculation section for calculating instruction values based on the variation part of the magnetic flux outputted from the magnetic flux calculation section 4 and the variation part of the shaft torque outputted from the shaft system calculation section 5. The reference number 8 indicates a sine wave generation section for generating a three phase sine wave voltage according to the instruction values outputted from the instruction value calculation section 7. The reference number 9 designates an amplifier and 10 indicates an electrical reactor.
Next, a description will be given of the operation of the conventional synchronous machine simulator shown in FIG. 18.
First, for the simulation of the synchronous machine, the A/D conversion section 1 performs the A/D conversion. During the A/D conversion, the real instantaneous values of analogue of both a three phase analogue voltage and a three phase analogue current of analogue are converted into the digital values thereof.
When the A/D conversion section 1 converts the three phase voltage and the three phase current into the digital values thereof, the exciting system calculation section 3 calculates the exciting voltage and an exciting current of the synchronous machine based on the three phase voltage and the three phase current in digital form. In addition, when the A/D conversion section 1 converts the three phase voltage and the three phase current into the digital values thereof, the d-q axis conversion section 2 performs the d-q axis conversion operation for the three phase voltage and the three phase current in digital form and generates and outputs the direct voltage and the direct current.
When the d-q axis conversion section 2 outputs the direct voltage and the direct current and when the exciting system calculation section 3 outputs the exciting voltage and the exciting current, the magnetic flux calculation section 4 calculates a variation part of the magnetic flux of the synchronous machine by using the direct voltage, the direct current, the exciting voltage, and the exciting current.
Furthermore, when the magnetic flux calculation section 4 outputs the variation part of the magnetic flux of the synchronous machine, the shaft system calculation section 5 calculates a variation part of the shaft vector of the synchronous machine based on the variation part of the speed governor system that has been calculated by the variation part of the magnetic flux and the speed governor calculation section 6.
After the magnetic flux calculation section 4 outputs the variation part of the magnetic flux of the synchronous machine and after the shaft system calculation section 5 outputs the variation part of the shaft torque, the instruction value calculation section 7 calculates instruction values based on the variation part of the magnetic flux and the variation part of the shaft torque and then outputs the instruction values to the three phase sine wave generation section 8. Thereby, the three phase sine wave generation section 8 generates a three phase sine wave voltage according to the instruction values in order to perform the simulation of the synchronous machine.
Thus, the conventional synchronous machine simulator has the configuration described above. Because the instruction values are generated based on the variation part (as a variation part of the electrical system) of the magnetic flux of the synchronous machine and the variation part (as a variation part of a mechanical system) of the shaft torque of the synchronous machine and because those instruction values are calculated based on the direct voltage and the direct current that are converted by the d-q axis conversion operation, there is a drawback that it is difficult to simulate the transient state of the AC electrical system accurately. For example, there is the conventional drawback in which it is difficult to generate double-frequency transient AC currents and transient DC currents, that may be generated originally, in symmetrical faults happened near the terminals of the synchronous machine, and it is also difficult to generate triple-frequency transient AC currents and the like, that may also be generated originally, in unsymmetrical faults happened near the terminals of the synchronous machine.